I5 GT Turbos 2871 / 3071 / 3076 / 3082 / 3582

[Rusty]

Sigh, limiting boost production in low to mid range, a generic map is not going to be as aggressive as a live map with a car running non stock rods.

Sounds like we are in agreement then

What about the issue of surge on 3071 then? 2871 I was aware was a PITA but wasn't aware of 3071 issues.

[A80Avant]

yes i understand that,
but the trend is that any turbo bigger than OEM RS2 should be going with new rods.It was not just a suggestion from many(if not all) and as i say the reason for that is the increased torgue on low range.

I just seem to feel that this trend is now slowly changing, and people that want to get a bigger turbo than RS2 are not necesserally needed to change the rods,and not changing them is not a bad thing nor would a map be a whole of a lot different than what a map to a stronger rod car would have.

To make things more obvious:
IF most I5 cars can get a good clear 1.9bar or 2bar on a 2871 or 3071R turbo after 4000rpm, would that be enough to keep the OEM rods in safety as far as torgue is concerned? Would 550Nm of torgue @ 4500rpm for example be adequate on the OEM rods? If so,then i believe that anyone with a stock bottom end could get a turbo like that and have no worries about bending a rod.

However 2 years ago, a statement like that in this forum would have been more or less discouraged as back then these turbos were thought to be spooling clearly and easily from 3000rpm and the fact that they are bigger than the RS2 turbo made all of us think that they could indeed cause problems with rods.

As far as im concerned,im glad i changed the rods anyway as im addicted to power and i want some better turbo now,but all im saying is that someone that has a view of getting one of these turbos i bet it would be safe to indroduce the boost gradually up until 4000rpm and then keep a high boost up to the red line so long as the EGTs permit it. It would be a good and safe result

[EspenW]

Rod failure from compressive load is dependent on peak cylinder pressure. Increasing torque output will increase average cylinder pressure, but not necessarily peak cylinder pressure. It depends on whether the torque is made from flow, boost, timing, longer stroke, etc. Different fuels will also produce different peak pressures. Thus, peak torque is just a rough guideline for risk of failure.
Point of failure from tensile load is a lot easier to pinpoint, especially in a NA engine. In a turbo engine, turbos actually helps protecting the rods from tensile failure at high rpm (by providing an opposing force through gas load and exhaust back pressure).
Installing stronger (and lighter) rods if the engine is apart is a given. Good insurance and allows higher rev limits than stock rods. Note that overrevving rods can take them into plastic deformation, thus radically weakening them, then bend them on the power stroke, or during mild detonation, making it appear that their failed from compressive load only.

[gnutz2]

That's one of the best 3071r dyno plots I've seen, if your saying you have 368 at the wheels it equates to 450-460 at the crank.

There's more to be had as you can run 1.9 to 2.0 bar max and then run 1.7 to redline

Why only run 1.7 bar to redline.

The compressor map shows up to 3 bar at the top end

look

[gnutz2]

I run my 35R up to 2.2 bar at top end.

[20vQC]

I like that map of the GT35 with that comp housing... you get 79% of efficiency between (approx.) 1.35 to 2.55 bars of pressure. It obviously depends on the air flow required.

[A80Avant]

360-370hp at the wheels is not more than 430hp at crank. at least according to the calculations i get through the PB

[Billman]

Why only run 1.7 bar to redline.

The compressor map shows up to 3 bar at the top end

look

yes but on the 5 cyl turbo you are going to be with 2 bar at the redline way out of the efficiency of the compressor.

[Billman]

I run my 35R up to 2.2 bar at top end.

If i use Paul's Excel correctly then you are with this turbo and 2.2bar at the redline also way out of the efficiency of your turbo. Dont see only the PR -1 bar (atmo) but also the pressurelossen on you piping ect.

[Billman]

for comparison reasons here is a map of a holset compressor (if my info is correct it is the same as on the small HX40 with 55-56mm Inducer and 82 exducer).

[IMG][/IMG]

[gnutz2]

The 72 percent efficiency island goes up to 2.6 bar so i would run it up to that pressure at redline, granted it drops down to 65 percent at 3 bar.

Just the same as the efficiency on the 35R map is 72 percent up to 2.2 bar.

[EspenW]

360-370hp at the wheels is not more than 430hp at crank. at least according to the calculations i get through the PB

Totally depends on type of dyno. 370awhp on a MAHA would mean close to 600hp at the flywheel (according to the MAHA dyno).

[A80Avant]

i was referring to the actual number if the losses were added to it.Not the procedure from which it was made from.
I just think that a rough calculation that adding 100hp to a whp number we get from any type of dyno for a 4x4 car is completelly wrong.

[Billman]

@Gnutz

OK, to show it to you graphically see the gray dots. They show where you oporate your turbo if lets say you run 2 bar all the way from 3000-7500.

[IMG][/IMG]

[gnutz2]

I see what you mean but i said at redline you can run the boost at 2.2.

You would never get 2.2 bar at 3000 rpm.

More like 1 bar at 4000 rpm and it climbs from there and puts the gray dots on the compressor map to the right side of the surge line.